Revert libxml2 behavior in Nokogiri gem that could cause XSS

Name: nokogiri
Version: 1.8.2
Advisory: CVE-2018-8048
Criticality: Unknown
URL: sparklemotion/nokogiri#1746
Title: Revert libxml2 behavior in Nokogiri gem that could cause XSS
Solution: upgrade to >= 1.8.3

Gemfile.lock

@@ -271,7 +271,7 @@ GEM
     mustermann (1.0.3)
     newrelic_rpm (5.0.0.342)
     nio4r (2.3.0)
-    nokogiri (1.8.2)
+    nokogiri (1.8.4)
       mini_portile2 (~> 2.3.0)
     oauth (0.5.4)
     oauth2 (1.4.0)